Iron plating method and composition



United States Patent 3,404,074 IRON PLATING METHOD AND COMPOSITION Otto J. Klingenmaier, Warren, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Filed Mar. 4, 1965, Ser. No. 437,276 7 Claims. (Cl. 20425) ABSTRACT OF THE DISCLOSURE An antipitting agent for iron plating baths is used which eliminates the necessity for maintaining ferrous ion solutions substantially completely free of ferric ions. The antipitting agent is a condensate of an aromatic sulfonic acid with an aldehyde in which the condensate has the general graphical formula (ARA')SO M, wherein R is an aliphatic nucleus, A and A designate aromatic groups containing naphthalene rings joined to the aliphatic nucleus, and 50 M designates at least one free sulfonic acid group in combination with a water-soluble, compound-forming radical M.

This invention relates to the electrodeposition of iron and more specifically to an antipitting agent for an iron plating bath.

It is extremely difficult to electrodeposit smooth, pit-free coatings of iron, particularly due to the process of ferric ions in the iron plating baths. I have found that ferric ion produce ferric hydroxide particles which adhere to the surface of the workpiece and provide sites upon which hydrogen can collect to prevent iron deposition. Continued de position on surrounding areas results in a pit in the surface of the iron deposit. If the ferric hydroxide deposits directly onto the basis metal, deposition may never occur there, so as to actually produce a hole in the resulting electrodeposit.

Q It is, therefore, an object of the present invention to provide an additive for iron plating baths which prevents pitting from occurring. It is also an object of this invention to provide a dispersant for ferric hydroxide in aqueous media. A further object is to provide an improved method for making iron plated articles.

. Other objects, features and advantages will become more apparent from the following description of preferred embodiments of this invention.

The invention comprehends electrodepositing an iron coating from an aqueous iron electroplating bath having an alkali metal salt of a condensed mono-naphthalene sulfonic acid. This salt disperses the ferric hydroxide normally produced during operation of the bath to prevent pitting in the iron deposit. While I have found that dispersing ferric hydroxide in the iron plating bath is a very effective means for reducing pitting, the usual dispersants simply are not satisfactory. The only antipitting agent which I have found that satisfactorily serves this purpose is a condensation product of an aromatic sulfonic acid from the naphthalene series and an aldehyde. Excellent results have been obtained with the condensate of a mono-naphthalene sulfonic acid and formaldehyde. I prefer to use a watersoluble salt of this condensate, such as an alkali metal salt, and more particularly the sodium salt, which has the following empirical formula:

4B A. l 1

This type of material is also described in United States Patents Nos. 2,046,757 Tucker and 2,046,758 Tucker, as

3,404,074 Patented Oct. 1, 1968 carbon black dispersants. United States Patent No. 2,056,924 Kabler describes such a material as a dispersant for zinc oxide. These patents describe this material as the condensate of a naphthalene sulfonic acid, or a homologue or derivative thereof, with formaldehyde, or its equivalent. About two moles of an aromatic sulfonic acid compound are reacted with each mole of formaldehyde under acid conditions. The aromatic compound is viewed as a derivative of polynaphthyl alkyls, or their homologues and are expressed by the general graphical formula:

wherein A and A designate two or more aromatic groups, which may or may not be alike, that contain naphthalene rings joined to an aliphatic nucleus R. The aliphatic nucleus R can be one alkyl group, or a plurality of straight chain or branched alkyl groups. The M designates at least one free sulfonic acid group in combination with a water-soluble, compound-forming radical. The radical is preferably an alkali metal ion, or even a hydrogen ion.

My antipitting agent is also commercially available from several sources under various trade names. It is available under the name Eloxan salt. It can also be obtained under the name Blancol N. It can also be obtained under the name Lomar PW. These commercially available materials can be directly used as purchased.

As previously indicated, my antipitting agent functions as a dispersant for ferric hydroxide. Ferric hydroxide is an impurity norm-ally present in iron plating baths formulated with ferrous salts. It is generated principally due to atmospheric oxidation of the ferrous ions to the ferric state. This oxidation is accelerated by the high temperature at which these baths are use-d.

Since my antipitting agent provides its improvement by dispersing ferric hydroxide, the minimum concentration necessary to produce the improvement depends on the ferric ion concentration in the bath. I

For a bath which has very little ferric ion present only about 0.25 gram per liter of my antipitting agent is needed to insure that no pitting will occur. This concentration, for example, Would be useful in a freshly prepared bath, as well as older bath solutions in which the ferric ion has either been chemically reduced or electrolytically removed. However, in general, I prefer to employ at least 0.5 gram per liter of my antipitting agent to provide a greater latitude in operation of the bath. Normally I prefer to employ a concentration of 0.5-1.0 gram per liter. 1.0 gram per liter of the antipitting agent is sulficient to disperse all the ferric hydroxide that one normally can otherwise tolerate in an iron plating bath. While concentrations up to 7.5 grams per liter can be effectively used to disperse ferric hydroxide, such concentrations are not generally employed. Ferric ion concentrations above what 1.0 gram per liter of my additive will protect, produce such a volume of ferric hydroxide that it fouls the plating filters, reduces anode efficiency by clogging the anode bags, etc. Thus, in general, one does not prefer to allow the ferric ion concentration to rise too high.

No special precautions are necessary when using my antipitting agent and it can be used in ferrous iron salt baths of virtually any concentration and temperature. Baths having a higher salt concentration are preferred since they tend to produce less stress in the deposits. In general and particularly with the ferrous chloride plating baths, I prefer to use as high a concentration as possible without encountering salting out problems. Ferrous chloride concentrations of approximatetly 62-66 ounces per gallon are convenient in this respect. The baths should be acid, of course, at least pH 1.2. For the ferrous chloride plating baths, a concentration of at least 0.05% hydrochloric acid should be used but 0.1% hydrochloric acid provides better bath control and reliability. In general, I prefer to employ about .2%-0.4% hydrochloric acid in a bath containing my additive. Acid concentrations in excess of 0.4% hydrochloric acid are to be avoided since they are unnecessary and likely to cause chemical attack of basis metals.

It is known that one can employ iron plating baths to produce hard, in excess of about Rockwell C 30, or soft iron deposits, depending on the current density and temperature used. My condensate not only protects against pitting but also reduces the deposition temperatures for both the hard and soft iron deposits by permitting higher bath concentrations to be employed. Soft iron deposits can now be consistently obtained at temperatures of approximately 180 F. to 190 F. instead of 190 F. to 210 F. Obviously even small reductions in the plating temperature, when the bath is near its boiling point, are quite significant.

The reduction in the hard iron deposition temperature is even more pronounced. Previously, the usual deposition temperature for producing hard iron deposits was about 160 F. to 170 F. With my additive I can produce hard iron deposits as low as 140 F.

Hence, my additive disperses the ferric hydroxide present and consistently completely eliminates pitting in soft iron deposits. Moreover, it usually completely eliminates pitting in hard deposits, and at least materially reduces it in all cases.

I have preferred to use my agent in iron plating baths formulated with ferrous chloride, with or without calcium chloride, rather than in the sulfate or sulfamate iron plating baths. Moreover, I prefer not to use a wetting agent when employing my additive. Best results have been obtained with a simplified ferrous sulfate bath. This simplified bath includes only ferrous chloride, hydrochloric acid and my antipitting agent. Both low and high concentration bathss of this type provide highly satisfactory results and are easy to operate. Two examples of these baths are as follows:

My antipitting agent has been found to be particularly beneficial in iron plating baths used to produce wearresistant iron coatings on aluminum surfaces, such as the wear surfaces of aluminum pistons. In producing an iron deposit on aluminum one would first pretreat the aluminum surface to receive the iron deposit. Any of the known and accepted pretreatments can be used. However, one which is particularly effective involves treating it with a strong nitric acid-hydrofluoric acid etch, rinsing it and then immersion zinc plating it. After the Zinc plating, it is rinsed and a lower pH cyanide copper strike, less than 0.1 mil in thickness, is applied. After copper plating, it is rinsed, dipped in dilute hydrochloric acid, rinsed agian and then placed in the iron plating bath with current on. It is preferred to immerse it in the iron plating bath with current on to prevent the thin copper coating from dissolving in the bath before iron deposition commences. A cathodic current density of approximately 100-125 amperes per square foot can be used to deposit a hard iron coating. If one desires to protect the iron deposit for storage and the like, a thin tin coating can be applied. In such instance, one would rinse the part after iron plating, dip it in dilute hydrochloric acid, rinse again and then immerse it in a tin electroplating bath. The usual alkaline potassium stannate-potassium hydroxide electroplating bath can be used.

While this invention has been described in connection with certain specific examples thereof, no limitation is intended thereby except as defined in the appended claims.

I claim:

1. An iron plating bath comprising an acid aqueous solution containing a ferrous iron salt and at least about 0.25 gram per liter of a water-soluble salt of an alkyl condensed naphthalene sulfonic acid having a general graphical formula (AR-A)SO M, wherein R is an aliphatic nucleus, A and A designate naphthalene rings joined to the aliphatic nucleus, and $0 M designates at least one free sulfonic acid group in combination with a water-soluble, compound-forming radical M.

2. An iron plating bath comprising an acid aqueous solution containing a ferrous iron salt and at least about 0.25 gram per liter of the sodium salt of a formaldehyde condensed mono-naphthalene sulfonic acid having a general graphical formula (AR-A)SO M, wherein R is -CH A and A designate naphthalene rings joined to -CH and M designates at least one free sulfonic acid group wherein M is Na.

3. An iron plating bath comprising an acid aqueous solution containing a ferrous iron salt and, as a pit preventative, from small but effective amounts up to about 7.5 grams per liter of a water-soluble alkali metal salt of the condensation product of a sulfonic acid from the paththalene series and formaldehyde, said condensate having a general graphical formula (AR-A)SO M, wherein R is -CH A and A designate naphthalene rings joined to CH and $0 M designates at least one free sulfonic acid group wherein M is alkali metal.

4. An aqueous iron plating bath containing at least about 25 ounces per gallon ferrous chloride, at least 0.05%, by volume, free hydrochloric acid, at least about 0.25 gram per liter of an aromatic sulfonic acid-aldehyde condensate having the general graphical formula wherein R is an aliphatic nucleus, A and A designate aromatic groups containing naphthalene rings joined to the aliphatic nucleus, and $0 M designates at least one free sulfonic acid group in combination with a watersoluble, compound-forming radical M.

5. An iron plating bath comprising at least about 25 ounces per gallon ferrous chloride, at least 0.05% by volume, free hydrochloric acid, about 0.5-1.0 gram per liter of a soluble condensate of mono-naphthalene sulfonic acid and formaldehyde, and water, said condensate having a general graphical formula (ARA)SO M, wherein R is CH A and A designate naphthalene rings joined to -CH and $0 M designates at least one free sulfonic acid group in combination with a Watersoluble, compound-forming radical M.

6. The method of iron plating which comprises immersing a metal part in an iron plating bath comprising an acidified aqueous solution containing a ferrous iron salt and at least about 0.25 gram per liter of the alkali metal salt of the condensate of mono-naphthalene sulfonic acid and formaldehyde, and applying a negative potential to the part immersed in said bath to electrodeposit iron thereon, said condensate having a general graphical formula (A--R-A')SO M, wherein R is --CH A and A designate naphthalene rings joined to -CH and $0 M designates at least one free sulfonic acid group wherein M is alkali metal.

7. The method of making an improved wear-resistant coating on an aluminum piston which comprises preparing the aluminum surface for iron deposition, immersing the part while under a negative potential in an iron plating bath containing about 62-6 6 ounces per gallon of ferric chloride, about 0.2%-0.4%, by volume, free hydrochloric acid, about 0.5-1.0 gram per liter of sodium salt of a formaldehyde condensed mono-naphthalene sulfonic acid, and water, said condensate having a general graphical formula (AR-A')SO M, wherein R is CH A and A designate naphthalene rings joined to --CH and SO M designates at least one free sulfonic acid group wherein M is Na, said bath being at a temperature of about F. to F., and continuing to apply said negative potential to said part to induce thereon a cathodic current density of approximately 100- 5 6 125 amperes per square foot to electrodeposit a coating 3,067,243 12/ 1962 Richter et a1 260505 of hard iron on said piston. 3,193,575 7/1965 Nebel et a1. 260 -505 R d OTHER REFERENCES cl-wees 5 Stoddard, William B. Jr.: "Iron Plating, transactions UNITED STATES PATENTS 0f the Electrochemical Society, vol. 84, pp. 305-312, 1,441,468 1/1923 Wills 29-4962 XR 1943' I 2,046,758 7/1936 Tucker etal 106--307 JOHN J W Erammer- 2,199,806 5/ 1940 Mitchell M. 260-605 G. KAPLAN, Assistant Examiner.

U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, 0.0. 20231 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,404,074 October 1, 1968 Otto J. Klingenmaier It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1 line 28 "process" should read presence 1; 29, "ion" should read ions Column 3, line 36, "bathss" should read baths line 57, "agian" should read again Column 4, line 20, "path" should read naph Signed and sealed this 17th day of February 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, J r.

Commissioner of Patents Attesting Officer 

